The Volcano rabbit (Romerolagus diazi) is an endemic species of Mexico, in danger of extinction, restricted to the central part of the Mexican transvolcanic belt. Considered like primitive species by its morphological characteristics, one faces a disminution in its free populations by destruction of its habitat mainly. It is one of the smallest rabbits of the world, it is of mainly diurnal activity, it lives in small groups, it does not present a defined reproductive stage but that remains in constant state of sexual acceptance once in puberty. The reproductive period includes all the year, although it is more intensive during the slighter summer and decrease during the winter. Its feeding consist mainly of grass. The present work is a description of the main biological aspects of the species, as morphology, behavior, feeding, distribution, habitat and with greater emphasis in the reproductive aspects and of conservation of the same one.